铁路无砟轨道水泥乳化沥青砂浆吸振与隔振特性

采用加速度计测定了冲击荷载作用下普通混凝土与水泥乳化沥青砂浆（CA砂浆）试件以及试件下部钢板的振动加速度随时间的变化,并用落锤法对比了普通混凝土与CA砂浆的抗冲击破坏特性.研究表明：普通混凝土受到冲击后,其振动加速度随时间衰减不明显,且振动时间较长,其下部钢板也有类似规律;CA砂浆受到冲击后,其振动加速度表现为3个明显的衰减阶段,振动时间也要短于普通混凝土,同样CA砂浆下部钢板也有类似规律;与普通混凝土相比,CA砂浆表现出较好的吸振与隔振功能.抗冲击破坏的结果表明,CA砂浆的抗冲击性能优于普通混凝土.     

On education

The following observations are intended only to outline some concerns about, and to offer observations on, the teaching of design disciplines in the University of Buenos Aires and to rehearse the current educational challenges relating to achieving the standards expected of a professional graduate competent to improve our environmental demands.     

Au/TS‐1 catalyst for propene epoxidation with H2/O2: A novel strategy to enhance stability by tuning charging sequence

For propene epoxidation with H₂ and O₂, the catalytic performance of Au/TS‐1 catalyst is extremely sensitive to preparation parameters of deposition‐precipitation (DP) method. In this work, effect of charging sequence in DP process on catalyst structure and catalytic performance of Au/TS‐1 catalyst is first investigated. For different charging sequences, the compositions of Au complexes (e.g., [AuCl(OH)₃]^?) and pore property of TS‐1 (i.e., with or without H₂O prefilling micropores) could affect the transfer of Au complexes into the micropores, resulting in different Au locations and thus significantly different catalytic performance. Notably, when TS‐1 is first filled with H₂O and then mixed with Au complexes, the reduced Au/TS‐1 catalyst could expose Au nanoparticles on the external surface of TS‐1 and show high stability. The results provide direct evidence showing that micropore blocking is the deactivation mechanism. Based on the results, a simple strategy to design highly stable Au/Ti‐based catalysts is developed. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3963–3972, 2016     

Functionalized galactoglucomannan‐based hydrogels for the removal of metal cations from aqueous solutions

New types of hydrogels derived from O‐acetyl galactoglucomannan (AcGGM) hemicellulose have been synthesized and characterized. The objective of this work was to analyze the sorption capacity (S) of three types of hydrogels containing AcGGM derivatives incorporated into the carboxylic groups of the polymer chain in the AA hydrogel, sulfonic groups in the APA hydrogel, and amide groups in the acrylamide (Aam) hydrogel. These hydrogels are capable of interacting and removing ions such as cadmium [Cd(II)], copper [Cu(II)], lead [Pb(II)], nickel [Ni(II)], and zinc [Zn(II)]. The results show that AA and Aam hydrogels had a lower sorption capacity of ions compared to the APA hydrogel, which had a high sorption capacity. The maximal sorption capacity was determined by the successive enrichment method, obtaining Pb(II) amount of 48.3 mg/g of AA hydrogel, 65.8 mg/g of APA hydrogel, and 40.8 mg/g of Aam hydrogel. Hence, Pb(II) ions are greatly retained by the three hydrogels. These results are promising for the development of new materials with potential applications in metal ion removal. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44093.     

Fabrication and Property of Mullite Whiskers Frameworks with an Ultrahigh Porosity by Expandable Mesocarbon Microbeads

Mullite whiskers frameworks with an ultrahigh porosity were fabricated by the vapor‐phase reaction of AlF₃, Al₂O₃, and SiO₂ and adding expandable mesocarbon microbeads (MCMB) as a pore‐forming agent. A large volume expansion of 122% for MCMB due to its layered structure occurred during the formation of mullite whiskers, resulting in the expansion of samples and high porosities of 87.7%–98.2% at 50–90 wt% MCMB contents. Perfect whiskers and a lap‐joint structure formed due to the formation of mullites through the vapor‐phase reaction. A bimodal pore structure was achieved from the spaces of the whiskers framework and burning of the expanded MCMB. High compressive strengths of 1.7 to 5.4 MPa were obtained for the porous mullite at porosities of 94.2%–87.7%, which suggested a rigid structure; these strengths at the ultrahigh porosities are attributed to the merit of the framework with high strength whiskers and their strong bonding.     

Influence of Microstructure and Surface Activation of Dual‐Phase Membrane Ce0.8Gd0.2O2−δ–FeCo2O4 on Oxygen Permeation

Dual‐phase oxygen transport membranes are fast‐growing research interest for application in oxyfuel combustion process. One such potential candidate is CGO‐FCO (60 wt% Ce_0.8Gd_0.2O_2?δ–40 wt% FeCo₂O₄) identified to provide good oxygen permeation flux with substantial stability in harsh atmosphere. Dense CGO‐FCO membranes of 1 mm thickness were fabricated by sintering dry pellets pressed from powders synthesized by one‐pot method (modified Pechini process) at 1200°C for 10 h. Microstructure analysis indicates presence of a third orthorhombic perovskite phase in the sintered composite. It was also identified that the spinel phase tends to form an oxygen deficient phase at the grain boundary of spinel and CGO phases. Surface exchange limitation of the membranes was overcome by La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) porous layer coating over the composite. The oxygen permeation flux of the CGO‐FCO screen printed with a porous layer of 10 μm thick LSCF is 0.11 mL/cm² per minute at 850°C with argon as sweep and air as feed gas at the rates of 50 and 250 mL/min.     

ForceSpinning of polyacrylonitrile for mass production of lithium‐ion battery separators

We present results on the Forcespinning^® (FS) of Polyacrylonitrile (PAN) for mass production of polymer nanofiber membranes as separators for Lithium‐ion batteries (LIBs). Our results presented here show that uniform, highly fibrous mats from PAN produced using Forcespinning^®, exhibit improved electrochemical properties such as electrolyte uptake, low interfacial resistance, high oxidation limit, high ionic conductivity, and good cycling performance when used in lithium ion batteries compared to commercial PP separator materials. This article introduces ForceSpinning^®, a cost effective technique capable of mass producing high quality fibrous mats, which is completely different technology than the commonly used in‐house centrifugal method. This Forcespinning^® technology is thus the beginning of the nano/micro fiber revolution in large scale production for battery separator application. This is the first time to report results on the cycle performance of LIB‐based polymer nanofiber separators made by Forcespinning^® technology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42847.     

Long-term stability of PEG-based antifouling surfaces in seawater

Poly(ethylene glycol) (PEG) is a hydrophilic polymer that has been extensively used in the biomedical and marine environment due to its antifouling properties. In the biomedical field, PEG has been successfully used to functionalize surfaces due to its resistance to cell and nonspecific protein adsorption. However, the long-term stability of PEG has limited its use in some areas. In the shipping industry, there is a great need for long-term solutions to keep the hulls of the ships fouling-free. The long-term stability of PEG in polydimethylsiloxane (PDMS) fouling-release coatings is studied here, in both accelerated laboratory tests and real seawater conditions. This article shows how PEG-based copolymers, which have been exposed in fouling-release coatings to real-life seawater conditions, are isolated and compared to those exposed to accelerated laboratory testing with successful results. The influence of the chemistry of the PEG compounds, the chosen laboratory degrading agents, and the possible degradation pathways and products are discussed.     

Dry Sliding Wear Properties of AZ31-Mg<Subscript>2</Subscript>Si Magnesium Matrix Composites

AZ31-Mg₂Si in situ composites were prepared from AZ31 Mg alloy and Si particles by a gravity casting method. Several parameters, such as Si content, normal load, and environmental temperature, were varied in order to study their effects on the composite dry sliding wear properties. Tensile properties and hardness of the composites were also investigated. The obtained results showed that the wear resistance, yield strength, and hardness of the AZ31-Mg₂Si composites increased with size and quantity of the Mg₂Si phase. However, when the environmental temperature increased from 25 to 190 °C, the composite wear resistance and ultimate tensile strength gradually decreased due to softening of the AZ31 matrix.